Method for pattern reproduction



Nov. 5, 1963 Filed Jan. 5, 1955 R. w. GUNDLACH METHOD FOR PATTERN REPRODUCTION FORM ELECTROSTATIC IMAGE OF PATTERN ON XEROGRAPHIC PLATE DEVELOP ELECTROSTATIC PATTERN WITH TACKIFIABLE DEVELOPING POWDER DEVELOPED POWDER PATTERN TRANSFER TO CARBON SHEET OF SPIRIT DUPLICATING SET SUPERPOSE MASTER SHEET OF SPIRIT DUPLICATING SET ON CARBON SHEET SEPARATE MASTER SHEET FROM CARBON SHEET FIG. I

3 Sheets-Sheet 1 IN V EN TOR.

ROBERT W. GUNDLACH BY MQQJ LF ATTORNEY Nov. 5, 1963 R. w. GUNDLACH 3,

METHOD FOR PATTERN REPRODUCTION Filed Jan. 5, 1955 s Sheets-Sheet 2 'IllIII/IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 5 INVENTOR.

ROBERT w. GUNDLACH ATTORNEY Nov. 5, 1963 R. w. GUNDLACH METHOD FOR PATTERN REPRODUCTION 3 Sheets-Sheet 3 Filed Jan. 5, 1955 INVENTOR.

ROBERT w. GUNDLACH QM A. 'Sim armv ATTORNEY FlG. I3

United States Patent M 3,109,366 METHOD FOR PATTERN REPRODUCTION Robert W. Gundlach, Spencerport, N.Y., assignor to Xerox Corporation, a corporation of New York Filed Jan. 3, 1955, Ser. No. 479,540 1 Claim. (Cl. fill-149.4)

This invention relates to the field of pattern reproduction and particularly to an improved method of and apparatus for affixing a predetermined dye pattern to the master sheet of a spirit duplicating set. V

In the process of liquid or spirit duplication, currently in general use for the production of copies of printed material, the copy to be reproduced is typed or written on the master sheet of a spirit duplicating set which includes a carbon sheet comprising alayer of dye containing material mounted on a relatively smooth backing sheet so that the dye containing material may readily be stripped therefrom. The dye containing layer of the carbon" sheet is arranged in juxtaposition to the master sheet, and the pressure of the type or writing instrument causes a quantity of dye from the carbon sheet to be deposited on the back of the master sheet in a pattern corresponding to that appearing on the front of the master sheet. When the master is thus prepared, it is placed on the rotating drum of a duplicating machine. As the copy paper is fed into the machine, it is moistened slightly, usually with an alcohol base dye solvent, as it comes in contact with either a roller or wick. Relatively little of the solvent is applied so that it evaporates quickly, but it is sufficient to pick up a thin layer of dye from the master and this dye remains on the copy paper in the form of the pattern deposited on the master sheet.

For the reproduction of typewritten copy, this process is quite adequate and is widely used, although the typist must exercise somewhat more than usual care in centering and laying out the work. A limitation of the process is that a constant typing pressure must be maintained in order to deposit a dye pattern of uniform thickness on the back of the master sheet. In the event the dye pattern is not of uniform thickness throughout, the thinner portions of dye are expended more quickly than theremainder of the dye pattern, with the result that the number of complete copies thatv can be made is limited by the thickness of the dye pattern in its thinnest portion. A further limitation is that the correction of typographical errors must be effected directly on the master sheet and requires substantially more time and elfort than in conventional typing practice, and usually results in noticeable defects in the finished copy. I

When the process is applied to the reproduction of written copy, line work, or art work, it becomes particularly cumbersome and unwieldy. In these cases, it is currently required that the desired copy be formed directly on the face of the master sheet in the exact form in which it is to be reproduced and that the writing or drawing pressure be maintained constant throughout in order to deposit a dye pattern of uniform thickness'on the reverse side of the master sheet in exact correspondence with the line copy pattern formed on the front. Such practice obviously requires the services of a skilled artist or draftsman and, at best, is extremely expensive and time consuming. Furthermore, in its present form,

Patented Nov. 5, 1963 tion Serial No. 479,453, filed concurrently with the present application, discloses an improved method for the preparation of spirit duplicating master sheets. 'In a typical application of this method, the copy to be reproduced is prepared in its final form on any convenient type of paper, and an electrostatic latent image of this copy is formed by the process of xerography on the photoconductive surface of a xerographic plate. An electroscopic developing agent, comprising minute powdered particles of resinous material and coloring matter, is then cascaded over this image so that the powder particles adhere to the latent image and form a powder particle pattern of the copy to be reproduced. This pattern is then transferred electrostatically to the surface of the dye layer of the carbon sheet of a spirit duplicating set and is held thereon by electrostatic attraction.

When the carbon sheet is thus prepared, the master sheet of the spirit duplicating set is superposed thereon whereby the powder particle pattern is effectively sandwiched between the master and carbon sheets. The assembled set is then placed between heated platens of a flat press wherein the entire outer surfaces of both sheets are uniformly subjected to controlled conditions of heat and pressure. In this step, the resinous particles of the powder pattern are tackified, i.e., reduced in viscosity and fused together in a mass that is internally cohesive and has a surface that is adhesive to many other materials, including both the dye layer of the carbon sheet and the master sheet of conventional spirit duplicating sets. The

desired conditions of heat and pressure are maintained for a predetermined time period to permit the tackified powder particles to be forced into the interstices of the master sheet and of the dye layer of the carbon sheet in a pattern corresponding to that of the copy to be reproduced. At the end of the predetermined time period, the duplicating set is removed from the press and is maintained in its assembled condition for a period of several seconds to permit the hardening of the resinous material. When hardening is complete, a portion of the dye layer of the carbon sheet, corresponding to the pattern of copy to be reproduced, is firmly bonded to the master sheet. Thereafter, the carbon and master sheets are separated and the adherent portion of the dye layer is literally pulled from the surface of the carbon sheet and remains affixed to the master sheet. The master sheet may then be used in the usual manner in a spirit duplicating machine.

Although the method disclosed in the above-mentioned application is basically sound and may be used for the formation of master sheets in many spirit duplicating applications, it has been found that it is not entirely satisfactory when used in conjunction with certain spirit duplicating sets that are currently on the market. In cases where dificulty is experienced, it is usually found that the dye layer of the carbon sheet is bonded with a material having a melting point in the temperature range in which the resinous material of the xerographic developing agent tackifies. When this occurs, minute particles of the dye layer, other than those within the copy pattern to be reproduced, occasionally adhere to the master sheet independently of the powder particle pattern and create an undesirable background effect on the finished copy. In general, these particles are quite small and the dye therein is expended after the production of the first five to fifteen copies of a given run. Thereafter, the remaining copies, which are formed from the substantially thicker portions of dye material corresponding to the desired copy pattern, are usually acceptable. Although this practice can be tolerated in certain instances, it limits the maximum number of copies that can be obtained from a master sheet, and is wasteful of time and material when considered from the standpoint of general application.

Upon investigation of the problem, it was found that the tackification and bonding of the powder particle pattern is primarily a problem of plastic deformation that is dependent upon the viscosity of the powder particles and the compressive stress applied in the bonding process.

On this basis it can be shown that a given deformation of the powder particle pattern is proportionately related to temperature, time, and pressure, and that optimum bonding of the dye layer pattern can be obtained by the proper control of these factors. However, the binders employed in the various dye. layers are also subject to deformation on the same basis. Thus, when the softening or melting points of the powder particles and the binders are in the same overlapping ranges, the creation of background on the finished copy is likely to occur unless the effect of at least one of the above factors can be varied to achieve differential results on either the powder particles or the binders.

No convenient method has been found for selectively varying the time during which a given pressure and temperature can be applied to either component. Differential pressures between the powder particle pattern and the uncovered portion of the dye layer are inherent because of the increased thickness resulting from the powder pattern itself, but, inasmuch as the powder pattern rarely exceeds one-half mil in thickness, the differences in pressure .are insufficient for any practical purpose. However, by selectively heating the powder pattern to a higher degree than the uncovered portions of the dye layer, it has been found that the powder pattern can be tackified independently without causing any deleterious effect on the uncovered dye layer, and that the desired portions of the dye layer can be bonded to the master set without the creation of background effect on the finished copy.

In order to extend the application of the invention disclosed in the above-entitled application so that the basic concept thereof may be applied to the preparation of master sheets when using substantially any type of spirit duplicating set, the principal object of the present invention is to provide an improved method of and apparatus for forming a predetermined dye pattern on the master sheet of a spirit duplicating set. A further object of the invention is to provide an improved method of and apparatus for bonding predetermined portions of the dye layer of the carbon sheet of a spirit duplicating set to the master sheet thereof. A further object is to provide an improved method of and apparatus for tackifying a pattern of powdered resinous material arranged between the master and carbon sheets of a spirit duplicating set. A further object of the invention is to improve the methodof and apparatus for the rapid, efficient, and economical production of master sheets for use in spirit duplicating processes.

Briefly, these and other objects of the invention are attained by selectively heating the powder particle pattern of the copy to be reproduced, substantially independently of the remainder of the spirit duplicating set, during the period in which pressure is applied to the set to effect the bonding of the dye layer to the master sheet. In this manner, the powder particle pattern is tackified without causing any deleterious or softening effect on the materials of the dye layer beyond the boundary of the powder particle pattern. This result is accomplished by forming the powder particle pattern of a material that is more of the invention, this is accomplished by forming the,

powder particle pattern of a material that is substantially 'more absorptive of infrared radiation than the dye layer and by exposing the duplicating set to a source of in- 4 I frared radiation during the pressure-applying period. I an alternate embodiment of the invention, this is accomplished by mixing finely-divided metallic material with the powder particles and exposing the duplicating set to a source of high frequency radiation during the pressureapplying period. In either case, pressure is applied to the, duplicating set in a press having an aperture or window that is substantially transparent to the type of radiation employed and through which the radiant energy is directed against the duplicating set.

The term tackified and the several variant forms thereof, used throughout the specification, are employed to define the condition of the powder particles that form the copy pattern when treated in a manner such that the individual particles soften and coalesce and in which state they become sticky and readily adhere to other surfaces. Although this condition necessarily requires a flowing together of the particles to effect a thorough fusion thereof, it is to be understood that the extent of such flowing is not sufficient to extend beyond the boundary of the pattern in which the particles are formed.

The method of the invention and a preferred device for implementing its application in the preparation of spirit duplicating masters are shown in the appended drawings, in which:

FIG. 1 is a flow diagram illustrating the several steps of the method of the invention, as applied in forming a predetermined pattern of dye material on the master sheet of a spirit duplicating set;

FIGS. 2 throughlO, inclusive, are schematic illustrations of the several steps of the method of FIG. 1, where? in:

FIG. 2 is a schematic plan view of a portion of a xerographic plate bearing an electrostatic image of a predetermined pattern formed thereon;

FIG. 3 is a schematic plan view of the xerographic plate of FIG. 2 wherein the latent image of the predetermined FIG. 7 is a schematic sectional view of the assembled spirit duplicating set arranged between the platens of a press in preparation for the tackifying and bonding operation;

FIG. 8 is a schematic sectional view'of the elements of FIG. 7 during the tackifying and bonding operation;

FIG. 9 is an enlarged view of a portion of the elements of FIG. 8, illustrating the absorption and reflection of radiant energy during'the tackifying and bonding operation; t v a FIG. 10 is a schematic sectional view illustrating the relationship of the several elements of FIG. 8 while the master and carbon sheets of the-spirit duplicating set are being separated;

FIG. 11 is an isometric view of a vacuum press that may be employed in practicing the method of the inven-' tion for the preparation of spirit duplicating master sheets;

FIG. 12 is a schematic sectional view of structural details of the vacuum press of FIG. 11;

FIG. 13 is an isometric view of an apparatus for tackifying and bonding a, powder particle p'attern in accordance with the method of the invention.

Spirit duplicating sets of the type with which the inven t1on may be employed are in wide commercialuse and many types of these sets are available from various manw facturers. In general, each set comprises a master sheet and a carbon sheet attached along one edge by a suitable hinge. The set may also include a separating sheet to prevent smudging of the carbon sheet during handling but which is removed prior to the actual use of the set. The master sheel usually comprises a firmly coherent, smooth surfaced sheet of translucent white paper that is readily receptive of impressions from typewriter type or conventional writing instruments. The carbon sheet comprises a firmly coherent, backing sheet of relatively glossy surfaced paper on which a thin layer of dye material or a combination of dyeintermediates or dye formers is uniformly spread.

The dye material is usually suspended in a wax coating or similar form of binder to make it adhere to the carbon sheet, and the particles of such coating are only loosely coherent with each other whereby the pressure applied by a writing instrument or type face readily detaches the impressed portion from the remainder of the dye layer. Also, since the carbon backing sheet has a smoother surface than-the master sheet, the dye layer in usual practice adheres more readily to the master sheet so that impressed portions are conveniently broken away from the carbon sheet when the components of the duplicating set are separated. Similarly, as in the above-mentioned application and in the present instance, the simultaneous bonding of the powder particle pattern to the master sheet and dye layer results in a firm bond between these materials that is much stronger than the bond between the dye layer and the carbon backing sheet so that the bonded portions of the dye layer are cleanly stripped from the backing sheet when the sheets are separated.

The xerographic formation and transfer of powder particle patterns of copy to be reproduced, as employed herein, is basically the same as that disclosed in Carlson Patent 2,297,691, issued October 6, 1942, wherein a plate comprising a coating of photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the light intensity which reaches them, thereby creating anelectrostatic latent image on or in the plate coating. Development of the image is effected with a finely divided material, such as an electroscopic powder, which is brought into contact with the coating and is held thereon clectrostatically in a pattern corresponding to the electrostatic latent image.

The developing agent employed may be of any convenient type suitable to the requirements of the particular application, the type disclosed in Patent 2,618,55 1, issued November 18, 1952, to L. E. Walk-up being illustrative of a form that may be used in most instances, although a wide variety of other resinous developing powders may be employed and may readily be adapted for use in the present invention. As disclosed in the' patent, the developer comprises a combination of coated glass bead carriers together with a toner powder which comprises particles of fusible resin in which a pigment such as carbon is bonded. These components are mixed together to establish an electrostatic charge on the powder particles that is of opposite polarity to the charge comprising the latent xerographic image whereby, when the developer is cascaded over an exposed Xerographic plate, the resin and carbon black particles adhere to the charged surfaces of the plate and form a powder image or pattern of the latent image previously formed thereon;

In the general application of xerography, the resin particles are subsequently bonded to the finished copy by the application of heat or solvent vapor and serve to secure the carbon black particles which provide the coloring matter in the finished copy. In the present application, the resin particles are tackified, as described below, and function as the bonding agent that unites the dye layer of the carbon sheet to the master sheet of the spirit duplicating set; whereas, the carbon black particles function primarily to increase the heat absorption characteristics of the powder when exposed to infrared radiation. In addition, the carbon black particles serve to produce a readily visible image whereby an operator may check the cornpleteness of the copy when it is formed on the xerographic plate, and when it is transferred to the spirit duplicating set.

In general, the dye layer formed on the carbon sheet of the spirit duplicating sets that are currently available comprises a dye material that may be any desired one of a variety of colors and usually has a glossy surface. Some of these sets have a very thin wax or metallic layer over the dye material to minimize soiling the hands of the operator. This coating usually increases the reflective characteristics of the carbon sheet. Recently, duplicating sets have been introduced commercially in which the dye layer includes substantially colorless or yellowish dye formers or dye intermediates which combine only in the presence of the solvent applied during the copying process to produce the ultimate color required on the finished copy. Thus, there is a wide range of heat and light reflective values in the surfaces of the dye layer materials currently available. However, all of these materials are more reflective than any of the various xerographic dev eloping powders currently in commercial use, wherein the high content of carbon black particles imp-arts substantially black body characteristics when considered from the standpoint of heat and light reflectivity.

Thus, when a pattern of xerographic developing powder is formed on the dye material of any currently available duplicating set, the dull, black, powder particle pattern is substantially more absorptive of infrared and/or visible radiation than the dye layer on which it is formed. When exposed to a source of infrared or visible radiation, the carbon black particles absorb a higher proportion of the radiant energy than the surrounding dye material and transmit the heat thus absorbed to adjacent particles of resinous material. In this manner, the resinous material is heated more quickly than the surrounding dye material and reaches the desired degree of tackification before the dye material is softened sufiiciently to adhere to the master sheet.

Referring to the drawings, the several steps of the method of the invention outlined in FIG. 1 are schematically illustrated in FIGS. 2 through 10, inclusive, wherein a x enographic plate 1 (see FIG. 2), comprising a layer of photoconductive material mounted on a conductive backing, is impressed with a reverse reading electrostatic image 2 of a predetermined pattern that is formed thereon by conventional xerographic processes. In this figure, plus signs are employed to indicate the electrostatic charge forming the latent image of the pattern after the plate is exposed. After exposure, a suitable powder particle developing agent, as described above, is cascaded over the plate whereby the electrostatic image 2 is transformed to a pattern of powder particles designated by're ference character 3 (see FIG. 3). Thereafter, powder pattern 3 is transferred electrostatically to the dye layer 4 of the carbon sheet 5 of a spirit duplicating set (see FIGS. 4

"then evacuated whereby atmospheric pressure causes platen 22 to press the duplicating set against platen 29 (as in FIG. 8), and serves to apply a uniform pressure over the entire surface of the duplicating set. Concomitantly, a source of infrared radiation, represented by heat raysin FIG. 8, is directed against platen 29. The radiation passes through the transparent material of the platen and through the translucent master sheet and is directed against the powder particle pattern as well as the unthereagainst is reflected'from the surface of the dye material (as in FIG. 9). Thus, in a given period of time appreciably more heat is absorbed by a unit area of the powder pattern than by a unit area of the dye material so that the powder pattern material is raised to its tackifying temperature, whereas the dye material is not raised to its softening temperature. Thus, the powder pattern material is heated independently without causing deleterious softening of the dye material.

Throughout this predetermined time period the pressure applied by the vacuum press is effective to force the tackified powder particles into the interstices of the opposed surfaces of the dye layer and the master sheet to form an adhesive layer between the sheets that corresponds to the outline of the pattern to be reproduced. At the end of the predetermined period, the radiant energy source is turned off and the vacuum in the vacuum press is released to remove the pressure applied against the duplicating set. When this occurs the powder pattern material hardens substantially instantaneously. When the master sheet and the dye layer of the carbon sheet are thus firmly united by the coalesced powder particles of the predetermined pattern, the sheets are separated either by stripping in the usual manner or by sliding the carbon sheet over a rod 8 or other rounded surface (as in FIG. 10), whereby the bonded dye particles are cleanly broken from the dye layer of carbon sheet 5. Master sheet 6, to which a dye pattern conforming to the predetermined pattern is firmly affixed, may now be used for producing copies in a duplicating machine in the usual manner.

Although a variey of devices may be employed to effect the tackification and bonding of the powder particle pattern in accordance with the method of the invention described above, a preferred apparatus for this purpose is shown in FIGS. 11 through 13, inclusive. Referring to FIGS. 11 and 12, there is disclosed a vacuum press of a type manufactured by the Miller-Trojan Company, Troy, Ohio, that includes a base member 20 having a substantially flat upper surface 21. Supported on surface 21 is a rubber mat, formed with a plurality of parallel ridges on its upper surface, that functions as the flexible platen of the press. Surrounding mat 22 is a peripheral gasket 23, having an inverted U-shaped cross-section, that is formed integrally with the mat and has an upper surface that is uniformlyraised abovethe surface of the mat. Vulcanized to the bottom of mat 22 is a flange member 24 in which is secured a short length of pipe 25 that passes through an opening in surface 21 and is connected by a hose 26 to a vacuum pump 27. The end of pipe 25 projects through an opening in mat 22 whereby, when pump 27 is operated, air is drawn from the space encompassed by gasket23. Hinged on base member 20 is a frame member 28 that supports a rectangular panel of plate glass 29 that functions as a transparent rigid platen for the press.

pounds per square inch, depending on the results desired.

As applied in the practice of the method of the inven tion, the carbon duplicating set, having a powder particle pattern arranged betweenthe master and carbon sheets, is placed on mat 22 with the master sheet uppermost.

' Frame 28 is then closed and pump 27 is operated to draw In operation, any article to whichpressure is to be applied is placed on mat 22 and frame 28 is rotated about its hinges until platen 29 rests on the upper surface of gasket23 and forms an air-tight seal therewith. When I pump 27 is operated to pull air from the space between a vacuum within the press and cause the entire duplicating set to be urged at uniform pressure against the undersurface of glass 29. At the same time, power is applied to a battery'of infrared lamps 30 that are arranged on a support 31 in a manner to provide substantially uniform radiation of the duplicating set. Power is applied to the lamps through a suitable timing switch 32, whereby the period of radiation may be limited at will. By this at.- rangement infrared radiation is absorbed selectively by the powder particle pattern to a greater extent than by the uncovered portion of the carbon sheet dye layer, whereby the powder pattern is tackified without causing undesirable softening of the dye layer.

Although duplicating sets may be employed in this method in their commercially available form with good results, the conventional paper master. sheet may, if desired, be replaced by a sheet of substantially transparent material to increase the effectiveness of the method. Various substances, such as Pliofilm, glassine, Kodopak, and cellophane, have been found expedient for use in this manner since the developing agents, referred to above, readily bond to any of these materials. The'only requirement being that the substance used have sufiicient body that it can be employed as the master sheet on a spirit duplicating machine. j

Pliofilm is a trademark of the Goodyear Tire and Rubber Company of Akron, Ohio, for a transparent sheeting material believed to be of rubber hydrochloride. composition. 'Kodopak is a trademark of the Eastman Kodak Company of Rochester, New York, for a transparent sheeting material believed to be of cellulosic ester com! position. e

A preferred arrangement of the source of infrared radi ation comprises six 75-watt infrared reflector-type lamps such as are conveniently available commercially, spaced about six to eight inches on centers, and from ten to twelve inches from the surface of the vacuum press. With this arrangement, the tackification and bonding of the dye layer is completed in approximately two minutes. This period is preferred because it permits an operator adequate time in which to prepare the following master sheet lamps of equivalent wattage may be used with substantially the same results. 7

Other modifications may also be made within the scope of the invention, if desired. For example, glass platen 29 in frame 28 may be formed of infrared transparent glass or any other diathermanous' material to conduction heating. Also, if desired, the vacuum press described above may be replaced by one having a rigid lower platen and a flexible transparent upper platen with a suitable gasket arranged therebetween. Similarly, the

invention is not limited to the use of a vacuum press since external pressure may be applied eitherabove or below the spirit duplicating set, should it be desired to.

apply greater pressures than those obtainable with a' vacuum press. Obviously, any such device that permits the application of radiant energy during the pressure} applying period is within the scope of the'invention.

In the alternate embodimentwof the method of the invention, finely-divided metallic particles,'preferably of saeasee iron, are mixed with the developing agent prior to the formation of the powder particle pattern illustrated in- FIG. 3. When this is done the assembled spirit duplicating set is placed in a press, as above, and is radiated from a source of radio frequency energy instead of with infrared radiation. In this arrangement the eddy currents created in the metallic particles generate sufficient heat to tackify the adjacent resinous particles in the powder pattern Without causing any heating effect on the uncovered portion of the dye layer, and the press functions to effect bonding, as above.

Although the method and the apparatus of the invention are described with specific reference to their application to the field of spirit duplicating, it is apparent that they may readily be applied in other fields for the purpose of pattern transfer within the scope of the invention. For example, should it be desired that a direct reading pattern be formed on the master sheet, as for use in an offset printing process, the reverse-reading powder image on the xerographic platemay be transferred directly to the master sheet instead of to the carbon sheet, as described above. Thereafter, the process is carried out in the same manner by superposing the sheets, tackifying the powder pattern under pressure, and separating the sheets to pull a direct-reading image of pattern material from the carbon sheet. Similarly, numerous other applications of the invention Will be apparent to those skilled in similar or related arts whereby a desired pattern-forming material that is difficult of convenient application or handling may be bonded to a supporting sheet or layer by means of a common bonding agent that can be conveniently formed into the desired pattern by xerographic processesv Therefore, it is intended that all matter contained in this specification be interpreted in an illustrative sense, and that the invention be limited only as defined in the appended claim.

What is claimed is:

The method of forming a predetermined dye pattern on a master sheet of a spirit duplicating set comprising the steps of: I

(a) forming a tacki-fiable xerographic powder particle image of such predetermined pattern on the dye layer of the carbon sheet of a spirit duplicating set, the powder particles forming said image including a sufficient quantity of carbon black as to render said particles more absorptive of radiant energy than the material of said dye layer;

(b) superposing the master sheet of said set on the dye layer of said carbon sheet;

(c) placing said sheets in their superposed relation in a vacuum press having:

(1) a chamber including a flexible platen on which to support the sheets in their superposed relation,

(2) a second platen being rigid, transparent and closable over said superposed sheets to enclose said chamber substantially vapor tight about said sheets,

(3) a vacuum pump connected to within said chamber to evacuate air therefrom and cause pressing of the opposed surfaces of the master and carbon sheets into intimate pressure contact with the powder image therebetween,

(d) actuating said vacuum pump to effect a contact pressure between said sheets of between about 10 to 15 p.s.i.;

(e) while said vacuum is maintained in said chamber,

directing through said second platen infrared radiation from six infrared reflector-type lamps of Watts each spaced about 6 to 8 inches on center 12 inches from said surface of said second platen and for a period of about 2 minutes to effect tackification of the powder particles and the bonding thereof to the materials of said sheets;

(7) removing the superposed sheets after exhausting the vacuum from said chamber; and,

(g) separating said sheets by sliding the carbon sheet of said sheets over a cylindrical rod whereby an area of dye layer corresponding to the area of the predetermined pattern is separated from the carbon sheet and is aifixed to the master sheet.

References Cited in the file of this patent UNITED STATES PATENTS 679,740 Gerlack Aug. 6, 1901 2,073,033 Szasz Mar. 9, 1937 2,085,075 Neidich Oct. 5, 1937 2,254,483 Hess et a1. Sept. 2, 1941 2,270,578 Campbell Jan. 20, 1942 2,587,084 Anderson Feb. 26, 1952 2,616,961 Groak Nov. 4, 1952 2,622,053 Clowe et al Dec. 16, 1952 2,738,727 Dorman et a1 Mar. 20, 1956 2,740,895 Miller Apr. 3, 1956 2,808,777 Roshkind Oct. 8, 1957 FOREIGN PATENTS 916,413 Germany Aug. 9, 1954 

